Generally known sensors for measuring gases and vapors are optical filters containing a sensor material which reversibly changes color in the presence of a gas or vapor. This color change affects the transmittancy of the filter under the influence of the gases or vapors. These filters contain a mixture of an alkaline, or acid, color former, also known as a colorant, and a complementary compound. Triphenylmethane compositions, preferably crystal violet lactone, for example, can be utilized as color formers ("colorants"). These filters may also comprise colorants of the triphenylmethane system, preferably phthalein or sulphophthalein, which can be embedded in a matrix and provided with a carrier. The change in the transmittancy of the filter, under the effect of the gases or vapors, is converted into an electric signal and processed electronically. A filter such as generally described above is discussed in German Published Patent Application No. 35 06 686.
Metal complexes having ligands with hydrophobing properties are generally known. Examples of these metal complexes include: monodentate ligands, for example dimethyl formamide; bidentate ligands; chelate ligands, for example ethylenediamine and acetylacetone, podandens and macrocylenes such as crown ethers and cryptands.
A change in electrical properties, such as a change in the dielectric constant or the electrical conductivity of a material, can be utilized to measure, or sense, gases or vapors, see, for example, Sensorik, Springer Publishers, Heidelberg, 1986, pages 195-199. This effect can be utilized in a simple way, such as with a gas sensor in the form of a condenser, to measure the humidity of the air. In this type of sensor the water-adsorbing dielectric material is applied to metal electrodes. The second electrode of the condenser is applied to the dielectric material, in the form of two engaging finger patterns, to form a comb-like structure. A dielectric material, which changes its dielectric constant under the effect of a gas, is superimposed over this comb-like structure. The corresponding change in the capacitance serves as a sensor signal.
The present invention provides a simple sensor system for gases or vapors, which enables the partial pressure or the concentration of virtually all solvents and gases to be continuously measured, even at low temperatures.